\begin{tikzpicture}[>=Stealth]
    \draw [->] (0, 0) -- (6, 0);

    \pic [transform shape] {interval={start=1, stop=5, height=0.5, infinity=true}};
    \draw [fill=white] (1, 0) circle(0.1) node [below=0.2em] {$a$};

    \pic [transform shape] {interval={start=3, stop=6, height=0.7, infinity=true}};
    \draw [fill=white] (3, 0) circle(0.1) node [below=0.2em] {$b$};
\end{tikzpicture}

